In recent years, the designers of long girder bridges in seismic areas have frequently opted for a continuous deck. One implication of this choice is that in many instances bridge abutments are called upon to carry large seismic forces, engaging the dynamic response of the soil–abutment system. To deal with this problem, this paper describes the formulation of a novel one-dimensional, inertial macroelement for simulating the dynamic behaviour of bridge abutments. The non-linear force–displacement relationship is characterised by a multi-surface plasticity model using a rigorous thermodynamic approach. The plastic response of the model is bounded by the ultimate capacity of the soil–abutment system that includes dissymmetry of the soil response in active and passive loading directions, while inertial effects transferred by the near-field approach embankment are simulated through appropriate participating masses in the macroelement formulation. The paper describes a straightforward calibration procedure of the proposed macroelement for horizontal, longitudinal loading of the abutment. The macroelement has been incorporated into a simplified, global, finite-element model of a multi-span girder bridge and validated through comparisons with results from a full three-dimensional (3D) dynamic time domain analysis under seismic loading. The inertial macroelement predictions of abutment deformations, axial deck loads and pier reaction forces are in very good agreement with the 3D soil–structure interaction model, and are achieved at much lower computational costs. The proposed inertial macroelement represents a significant improvement over existing simplified models based on linear response of the soil–abutment system.
The seismic performance of integral abutment bridges (IABs) is affected by the interaction with the surrounding soil, and specifically by the development of interaction forces in the embankment‐abutment and soil‐piles systems. In principle, these effects could be evaluated by means of highly demanding numerical computations that, however, can be carried out only for detailed studies of specific cases. By contrast, a low‐demanding analysis method is needed for a design‐oriented assessment of the longitudinal seismic performance of IABs. To this purpose, the present paper describes a design technique in which the frequency‐ and amplitude‐dependency of the soil‐structure interaction is modelled in a simplified manner. Specifically, the method consists of a time‐domain analysis of a simplified soil‐bridge model, in which soil‐structure interaction is simulated by means of distributed nonlinear springs connecting a free‐field ground response analysis model to the structural system. The results of this simplified method are validated against the results of advanced numerical analyses, considering different seismic scenarios. In its present state of development, the proposed simplified nonlinear model can be used for an efficient evaluation of the longitudinal response of straight IABs and can constitute a starting point for a prospective generalisation to three‐dimensional response.
This paper describes an original approach to the study of the seismic behaviour of bridge abutments. The proposed method incorporates a simplified description of the dynamic response of the bridge structure into a finite-element model of the soil–abutment system. Specifically, the dynamic behaviour of the bridge structure is described by a macro-element that simulates the loads transferred to the abutment during the seismic event. The macro-element is identified using a structural model of the bridge as a reference. This approach improves the current analysis methods based on sub-structuring, limiting at the same time the computational demand needed for a complete study of the soil–structure interaction. In the paper, the validity of the procedure is demonstrated comparing the results of the simplified approach with the results obtained from full three-dimensional dynamic analyses of idealised soil–bridge systems, using non-linear advanced constitutive models to describe the soil behaviour. Based on these results, a strategy is devised for the calibration of the bridge macro-element, making use of a limited number of input parameters.
Foundation piles can be used as a means for increasing the capacity of the foundations under static loads or, at the same time, can be regarded as an additional source of energy dissipation for the structure during strong motion. Under multiaxial loading, the ultimate capacity of a pile group is closely connected with the attainment of the flexural strength in the piles, which can in turn vary significantly according to the specific load path followed. Nonetheless, the design of piled foundations is still based on an independent evaluation of the vertical and horizontal capacities without accounting for the interaction between the several loads acting on the footing. To overcome this issue, in this paper a simplified numerical procedure for evaluating the capacity of piled foundations under multi-axial loading conditions is developed, which is based on the lower bound theorem of plastic limit analysis. On the basis of the numerical results, an analytical model of ultimate limit state surface is proposed, representing the force combinations that activate global plastic mechanisms of the soil-piles system. The identification of the ultimate surface necessitates a limited number of parameters having a clear physical meaning. The ultimate surface can lead to an optimised design of pile groups, allowing for a better control of the ultimate capacity as a function of the expected load patterns under static and dynamic conditions. In structural analysis, the ultimate surface can also be regarded as a bounding surface of a plasticity-based macroelement for piled foundations to account for the nonlinear features of the soil-pile system.
This paper proposes a multiaxial macroelement for bridge abutments that can be included in the global structural model of a bridge to carry out nonlinear dynamic analyses with very much smaller computational effort than can be achieved using continuum representations of embankment and foundation soil behaviour.
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